The invention relates to a process and a device for separation of absorbent/floating material from product mixes by means of float/sink separation.
From prior art there are known float/sink separators which are primarily used in the field of separation of plastics. Their mode of operation is the separation of a product mix into a floating fraction and a sinking fraction. Conventional float/sink separators operate on the principle of ensuring an efficient separation process with thorough mixing and wetting of the mix of solids to be separated, and a long dwell time in the separator. For this purpose, the material is usually placed in the separating medium (usually water) with intensive mixing, and repeatedly pushed below the surface of the separating medium by means of appropriate devices. By means of adequately large settlement basins and a long dwell time, it is possible to ensure that the sinking fraction can be adequately completely separated from the floating fraction. The disadvantage of this process is that it is not suitable for separation of absorbent/floating material from a product mix, because material that would otherwise float becomes saturated in the separating medium because of the long dwell time, and then sinks together with the heavier sink fraction.
From generic DE195 07 703 there is known a process and a device for separation of product mixes by means of float/sink separation, in which context, by means of nozzles arranged relatively far below the surface of the separating medium, a flow is generated. This is directed towards the surface of the water in order to drive any absorbent/floating material which has sunk below the surface of the separating medium, such as paper for example, back to the surface of the separating medium, where it is extracted from the device by means of a removal device. The disadvantage of this process is that there is nothing to prevent absorbent material from becoming saturated with the separating medium with the result that it sinks. In particular, the flow directed to the surface of the separating medium prevents the sinking fraction which is moving in the opposite direction from sinking down smoothly. Furthermore, after separation of the floating fraction, a further step is necessary in order to remove the absorbed separating medium from the floating fraction once again.
On this basis, the objective of this invention is to provide a process and a device for separation of absorbent/floating material from product mixes by means of float/sink separation, in which context it is largely possible to avoid saturation (with separating medium) of the absorbent material to be separated.
This objective is achieved according to this invention by means of a device with the characteristics of claim 1.
The advantage produced by these measures is that the absorbent material cannot become saturated with the separating medium, or only slightly so, during its brief dwell period in the separating medium, and is able to sink. Thus, a simple means is provided for its removal from the surface of the separating medium. Since the absorbent material is rapidly removed from the pickup point, it is possible to prevent a situation, furthermore, in which the upstream product mix presses it below the surface of the separating medium or in which the sinking fraction is prevented from sinking because of the absorbent material remaining at the pickup point.
The process developed for separation of absorbent/floating material and the corresponding device are ideally employed for separation of open-pored plastic foam materials. However, it is also possible to separate closed-pored plastic foam materials or other absorbent/floating materials whose density is less than that of the separating medium, from other materials. If in the case of open-pored foam materials a significant proportion of the pores are filled with air, then the foam particles will float on the surface of the separating medium. This is frequently the case after comminution of foam materials.
The subsidiary claims describe advantageous configurations and useful further developments of the main principles. If the absorbent/floating material is already saturated with a liquid, such as ink for example, before float/sink separation, then a particularly advantageous configuration of this type can be achieved by separation of a proportion of the liquid, for example by means of a vibrating filter, as a stage preliminary to float/sink separation. In this way it is also possible to make absorbent material which is extensively saturated with liquid adequately buoyant for subsequent float/sink separation.